2.1 Field of the Invention
The present invention relates to light-emitting materials and devices constructed using such materials. More specifically, the present invention relates to organic, electroluminescent materials and associated devices. The present invention has applications in the areas of materials science, organic chemistry, and electronics.
2.2 The Related Art
Makers of electronic devices that produce visual information, such as computers, are working intensely to develop lightweight display devices that provide brighter, sharper pictures at lower manufacturing cost. The drive to lighter, cheaper, better displays has lead to the development of flat-panel displays (xe2x80x9cFPDsxe2x80x9d) that are commonly used in laptop computers and include a growing share of the desktop computer display market. FPDs are almost exclusively liquid crystal displays (xe2x80x9cLCDsxe2x80x9d). However, LCD technology has shortcomings, including weak brightness and large power requirements.
One alternative to LCDs are electroluminescent (xe2x80x9cELxe2x80x9d) displays. EL displays use the luminescense of a solid film that is produced when a voltage is applied to the solid film. Referring to FIG. 1, which illustrates the process generally, the electroluminescent material (xe2x80x9cEMLxe2x80x9d) is placed between a cathode and an anode. The application of an electric potential (typically xcx9c100 MV/m) injects holes into the highest occupied molecular orbital (xe2x80x9cHOMOxe2x80x9d) or valence band (xe2x80x9cVBxe2x80x9d) of the EML from the anode, and electrons are injected into the lowest unoccupied molecular orbital (xe2x80x9cLUMOxe2x80x9d) of the EML or conduction band (xe2x80x9cCBxe2x80x9d). The recombination of the electrons and holes in the EML causes the emission of light from EML.
To increase light output efficiency, a hole transport layer (xe2x80x9cHTLxe2x80x9d) and/or electron transport layer (xe2x80x9cETLxe2x80x9d) are provided to increase the efficiency of hole (electron) injection and recombination in the EML. This has led to the design of EL displays having the general structure shown in FIG. 2 at 200. There, an electrode 202 is coupled with an electron transport layer 204. ETL 204 is coupled with electroluminescent layer 206, which, in turn, is coupled with hole transport layer 208. HTL 208 is coupled with electrode 210. Electrodes 202 and 210 are connected by contacts 212 and 214 that are each coupled to a source 216.
Presently, EL displays are fabricated using either inorganic materials, such as manganese (Mn)-doped zinc sulfide (ZnS), or organic materials such as polyphenylene vinylene (xe2x80x9cPPVxe2x80x9d) and its derivatives. However, no satisfactory EL material has been developed for widespread applications. Although inorganic EL displays can provide high performance and durability, they suffer from large power requirements and expensive, low-throughput fabrication processes. Thus, inorganic EL displays have been relegated largely to niche applications, such as military and medical applications. Organic EL displays, on the other hand, can be fabricated more cheaply and simply than inorganic EL displays, but suffer from relatively poor performance.
Thus, a need remains to provide an EL display having a cost/performance profile that is suitable for the general marketplace. Such a device will require materials that are relatively inexpensive and simple to prepare compared to inorganic EL displays while providing comparable performance characteristics. The present invention meets these and other needs.
The present invention provides organic electroluminescent materials having desirable efficiency, weight, and durability properties, as well as devices made from such materials. The materials provided by the present invention are relatively straightforward to make, thereby being economically attractive. In addition, the light-emitting organic materials of the invention have been found to have performance characteristics comparable to inorganic light-emitting devices. Thus, the organic electroluminescent materials and devices of the invention will be appreciated by those of skill in the materials and electronics arts to address important needs in those fields.
In a first aspect, the present invention provides an electroluminescent device. The device of the invention includes, in one embodiment, an anode and a cathode. An organic electroluminescent material is electroluminescently conductively coupled directly with the anode and cathode such that the organic electroluminescent material emits light upon the application of a voltage across the anode and cathode. The organic electroluminescent material includes an organo-siloxane polymer. The main chain of the organo-siloxane polymer comprises an organic component that can be chosen from the group alkenyl, alkynyl, aralkyl, aryl, heteroaralkyl, and heteroaryl, and which can be substituted with hydrogen, alkyl, aryl, heteroalkyl, heteroaralkyl, nitro, cyano, hydroxy, alkoxy, aryloxy, thio, alkythio, arylthio, amino, halogen, dialkylamino, diarylamino, diaralkylamino, arylamino, alkylamino, arylalkylamino, carbonyloxy, carbonylalkoxy, carbonylalkyloxy, alkylcarbonyloxy, arylcarbonyloxy, alkoxylcarbonyloxy, sulfonyl, or sulfonyloxy. The organic component includes at least two covalent bonds coupling the organic component to the main chain of the organo-siloxane polymer.
In one embodiment, the organic component is selected from the group consisting of alkylene, aralkylene, arylene, heteroaralkylene, and heteroarylene. In a more specific embodiment, the organic component is arylene or heteroarylene, and, still more specifically, arylene. More particular embodiments include those for which the organic component comprises a polycyclic aromatic carbon network containing between 2 and 7 fused aromatic rings. Still more particular embodiments are those for which the polycyclic ring system is selected from the group consisting of electroluminescent agents, hole transport agents, electron transport agents, and combinations thereof.
In some embodiments, the organic component is a polycyclic aromatic carbon ring system that functions as an electroluminescent agent. In a more specific embodiment, the organic component comprises anthracene. In a still more specific embodiment, the anthracene is coupled with a silicon atom in the main chain of the organo-siloxane polymer by at least one alkyl group. In one embodiment, the alkyl group has the formula xe2x80x94CH2(CH2)mCH2xe2x80x94, where m is an integer between 0 and 4. In another more specific embodiment, the anthracene is coupled with the main chain of the organo-siloxane polymer by two such alkyl groups. The alkyl groups can be situated at two symmetric positions on the anthracene. A specific example of one such substituted anthracene is that for which m is 1 and the alkyl groups are located at the opposing central carbon atoms of the anthracene molecule: 9,10-bis(trimethylene)anthracene: 
In another embodiment, the organic component comprises pentacene. In a still more specific embodiment, the pentacene is coupled with a silicon atom in the main chain of the organo-siloxane polymer by at least one alkyl group. In one embodiment, the alkyl group has the formula xe2x80x94CH2(CH2)mCH2xe2x80x94, where m is an integer between 0 and 4. In another more specific embodiment, the pentacene is coupled with the main chain of the organo-siloxane polymer by two such alkyl groups, which alkyl groups can be situated at symmetric positions on the carbon ring system. A specific example of one such substituted pentacene is that for which m is 1: 6,13-bis(trimethylene)pentacene: 
The electroluminescent material can further include a dopant, such as an electron transport material, a hole transport material, or a dye. The electron transport material, hole transport material, or dye can be provided individually or in combination. In one embodiment, the hole transport material can be, without limitation, a porphyrin or aromatic tertiary amine. In another embodiment, the dye can be, without limitation, coumarin, a rhodamine salt (e.g., rhodamine perchlorate), or perylene. In still another embodiment, the organo-siloxane polymer is cross-linked with oxygen atoms.
In another aspect, the invention provides an organic electroluminescent material comprising an organo-siloxane polymer in combination with an electron transport material, a hole transport material, or a dye. The electron transport material, hole transport material, or dye can be combined with the organo-siloxane polymer individually or in combination. The organic component of the organo-siloxane polymer is selected from the group consisting of alkenyl, alkynyl, aralkyl, aryl, heteroaralkyl, and heteroaryl, which can substituted optionally with hydrogen, alkyl, aryl, heteroalkyl, heteroaralkyl, nitro, cyano, hydroxy, alkoxy, aryloxy, thio, alkythio, arylthio, amino, halogen, dialkylamino, diarylamino, diaralkylamino, arylamino, alkylamino, arylalkylamino, carbonyloxy, carbonylalkoxy, carbonylalkyloxy, alkylcarbonyloxy, arylcarbonyloxy, alkoxylcarbonyloxy, sulfonyl, or sulfonyloxy. The organic component includes at least two covalent bonds coupling the organic component with the main chain of the organo-siloxane polymer.
In a more specific embodiment, the organic component comprises anthracene. In a still more specific embodiment, the anthracene is coupled with a silicon atom in the main chain of the organo-siloxane polymer by at least one alkyl group. In one embodiment, the alkyl group has the formula xe2x80x94CH2(CH2)mCH2xe2x80x94, where m is an integer between 0 and 4. In another more specific embodiment, the anthracene is coupled with the main chain of the organo-siloxane polymer by two such alkyl groups. The alkyl groups can be situated at two symmetric positions on the anthracene. A specific example of one such substituted anthracene is that for which m is 1 and the alkyl groups are located at the opposing central carbon atoms of the anthracene molecule: 9,10-bis(trimethylene)anthracene.
In another embodiment, the organic component comprises pentacene. In a still more specific embodiment, the pentacene is coupled with a silicon atom in the main chain of the organo-siloxane polymer by at least one alkyl group. In one embodiment, the alkyl group has the formula xe2x80x94CH2(CH2)mCH2xe2x80x94, where m is an integer between 0 and 4. In another more specific embodiment, the pentacene is coupled with the main chain of the organo-siloxane polymer by two such alkyl groups, which alkyl groups can be situated at symmetric positions on the carbon ring system. A specific example is 6,13-bis(trimethylene)pentacene.
In one embodiment, a hole transport material is included with the organic electroluminescent material. In one embodiment, the hole transport material can be, without limitation, a porphyrin or aromatic tertiary amine. In another embodiment, a dye is included with the organic electroluminescent material. The dye can be, without limitation, coumarin, a rhodamine salt (e.g., rhodamine perchlorate), or perylene. In still another embodiment, the organo-siloxane polymer is cross-linked with oxygen atoms.
In another aspect, the present invention provides an organo-siloxane polymer having a main chain including silicon, oxygen, and an organic component selected from alkenyl, alkynyl, aralkyl, aryl, heteroaralkyl, and heteroaryl. The organic component can be substituted optionally with hydrogen, alkyl, aryl, heteroalkyl, heteroaralkyl, nitro, cyano, hydroxy, alkoxy, aryloxy, thio, alkythio, arylthio, amino, halogen, dialkylamino, diarylamino, diaralkylamino, arylamino, alkylamino, arylalkylamino, carbonyloxy, carbonylalkoxy, carbonylalkyloxy, alkylcarbonyloxy, arylcarbonyloxy, alkoxylcarbonyloxy, sulfonyl, or sulfonyloxy. The organic component includes at least two covalent bonds coupling the organic component to the main chain of the organo-siloxane polymer.
In a more specific embodiment, the organic component comprises anthracene. In a still more specific embodiment, the anthracene is coupled with a silicon atom in the main chain of the organo-siloxane polymer by at least one alkyl group. In one embodiment, the alkyl group has the formula xe2x80x94CH2(CH2)mCH2xe2x80x94, where m is an integer between 0 and 4. In another more specific embodiment, the anthracene is coupled with the main chain of the organo-siloxane polymer by two such alkyl groups. The alkyl groups can be situated at two symmetric positions on the anthracene. A specific example of one such substituted anthracene is that for which m is 1 and the alkyl groups are located at the opposing central carbon atoms of the anthracene molecule: 9,10-bis(trimethylene)anthracene.
In another embodiment, the organic component comprises pentacene. In a still more specific embodiment, the pentacene is coupled with a silicon atom in the main chain of the organo-siloxane polymer by at least one alkyl group. In one embodiment, the alkyl group has the formula xe2x80x94CH2(CH2)mCH2xe2x80x94, where m is an integer between 0 and 4. In another more specific embodiment, the pentacene is coupled with the main chain of the organo-siloxane polymer by two such alkyl groups, which alkyl groups can be situated at symmetric positions on the carbon ring system. A specific example is 6,13-bis(trimethylene)pentacene.
In still another aspect, the present invention provides a method for fabricating an electroluminescent device in which an anode and a cathode are provided. The anode and cathode are coupled with an organic electroluminescent material that includes silicon-oxygen bonds under conditions effective to allow direct, electroluminescent conduction among the organic electroluminescent material, anode, and cathode such that the organic electroluminescent material emits light upon application of a voltage across the anode and cathode. Thus, the unique cross-linked organo-siloxane material provided by the present invention enables the production of more efficient and robust electroluminescent devices.
These and other aspects and advantages will become apparent when the Description below is read in conjunction with the accompanying Drawings.